The invention relates in general to a novel apparatus for classifying non-uniform particles and in particular, to a classifying apparatus including means to remove and collect fines or dust created during the classifying operation.
More specifically, the invention relates to an improved apparatus for pneumatically classifying mineral particles and mine run materials such as sand into a consistent particle size in separated fractions. The apparatus utilizes means to create a controlled flow of air through a series of classifying means to deflect free falling particles for separation according to size. The apparatus includes a fines removal and collection system to eliminate the presence of the very small or light particles which inherently form as a cloud of material within and in vicinity of a classifier during operation. The fines removal system includes means to extract the particles from the flow through the classifier to a precipitator for separation whereby the fines are collected and particle free air returns to the flow without disturbance to the classifying process.
In my prior patent, U.S. Pat. No. 3,288,284 for Method and Apparatus for Pneumatically Classifying Solids, issued Nov. 29, 1966, there is disclosed an improved system for classifying particles such as sand into separated fractions of highly uniform size. The apparatus disclosed in the patent is a significant improvement over the technique employed in the prior art and has accomplished highly effective results in use.
However, inherent in the pneumatic classification of many mineral particles and mine run materials such as by the apparatus of my prior patent is the formation of clouds of very fine material or dust which is referred to in the art as "fines". This phenomenon is created due to numerous conditions such as, for example, the physical properties of the material to be classified, the weight, density, and size of the smaller particles in the mass or deflection or bounce occurring during classification. Because a flow of pneumatic air is utilized to fractionize the particles according to size, the fines tend to laden the air stream passing through the classifying stages. Not only does the presence of fines or dust within the air stream interfere with accuracy of the classifying process, particularly after an extended operation, the material itself tends to clog up baffle plates which are used to maintain laminar flow through the apparatus and to thereby necessitate cleaning.
In addition to interfering with the operation of the classifier, the fines or dust also tend to escape from the apparatus to pollute the air of the surroundings as well as depositing material in the vicinity. Another problem associated with the previous systems for pneumatically classifying resulted because the prior system described in the patent and other apparatus are not in a closed system and are thus subject to atmospheric conditions around the apparatus. Because the apparatus often is situated out of doors, the presence of wind and other weather conditions can disturb the air flow circulating through the classifier and disrupt the accurate classifying of particles.
Accordingly, it is desirable to provide a classifier which achieves the highly efficient classification of solids as was possible in the apparatus of my prior patent within a closed system with removal of fines and dust in order that accurate classifying can be achieved during extended periods of service without pollution of the surroundings.